Reaction time (RT) is a pervasive dependent measure in many areas of psychological research. RT is pervasive because it can be an extremely useful source of evidence concerning a host of mental processes associated with perception, memory, attention, reasoning, judgment, problem solving, etc. However, the use of RT is frought with difficulties. It is possible to construct radically different models of mental functioning that predict similar effects on RT. So, without making strong assumptions about the organization of mental processes, RT frequently does not prove to be a highly diagnostic tool for answering certain.types of important theoretical questions, for instance, whether these processes yield outputs in a continuous stream, or in discrete quanta. A new experimental technique called speed-accuracy decomposition (SAD) overcomes many of the limitations of RT. By statistically decomposing distributions of RT trials and speed-accuracy tradeoff trials, this technique allows one to trace out the time-course of mental processes. Such information enables us to answer many important questions, such as whether process outputs are discrete or continuous. By using this technique to analyze subjects' performance in a broad variety of experimental tasks, it should be possible to derive a time-course "profile" for each task. Since processes with similar time courses should have certain architectural features in common, it should be possible to derive a general taxonomy of mental processes based on these profiles. Such a taxonomy could clarify relationships between theorizing in diverse areas of psychology, leading to new concepts and research ideas. These profiles and taxonomy could also provide a basis for diagnosing various forms of psychological and neurological pathology (e.g., if an individual's timecourse profile for a particular task does not conform to the standard for that task).